How is tb diagnosed?

Tuberculosis Screening

What is a tuberculosis (TB) screening?

This test checks to see if you have been infected with tuberculosis, commonly known as TB. TB is a serious bacterial infection that mainly affects the lungs. It can also affect other parts of the body, including the brain, spine, and kidneys. TB is spread from person to person through coughing or sneezing.

Not everyone infected with TB gets sick. Some people have an inactive form of the infection called latent TB. When you have latent TB, you don’t feel sick and can’t spread the disease to others.

Many people with latent TB will never feel any symptoms of the disease. But for others, especially those who have or develop weakened immune systems, latent TB can turn into a far more dangerous infection called active TB. If you have active TB, you may feel very sick. You may also spread the disease to other people. Without treatment, active TB can cause serious illness or even death.

There are two types of TB tests used for screening: a TB skin test and a TB blood test. These tests can show if you have ever been infected with TB. They don’t show if you have a latent or active TB infection. More tests will be needed to confirm or rule out a diagnosis.

Other names: TB test, TB skin test, PPD test, IGRA test

What is it used for?

TB screening is used to look for a TB infection in a skin or blood sample. The screening can show whether you have been infected with TB. It does not show if TB is latent or active.

Why do I need a TB screening?

You may need a TB skin test or TB blood test if you have symptoms of an active TB infection or if you have certain factors that put you at higher risk for getting TB.

Symptoms of an active TB infection include:

  • Cough that lasts for three weeks or more
  • Coughing up blood
  • Chest pain
  • Fever
  • Fatigue
  • Night sweats
  • Unexplained weight loss

In addition, some childcare centers and other facilities require TB testing for employment.

You may be at higher risk for getting TB if you:

  • Are a health care worker who cares for patients who have or are at high risk for getting TB
  • Live or work in a place with a high rate of TB infection. These include homeless shelters, nursing homes, and prisons.
  • Have been exposed to someone who has an active TB infection
  • Have HIV or another disease that weakens your immune system
  • Use illegal drugs
  • Have traveled or lived in an area where TB is more common. These include countries in Asia, Africa, Eastern Europe, Latin America, and the Caribbean, and in Russia.

What happens during a TB screening?

A TB screening will either be a TB skin test or a TB blood test. TB skin tests are used more often, but blood tests for TB are becoming more common. Your health care provider will recommend which type of TB test is best for you.

For a TB skin test (also called a PPD test), you will need two visits to your health care provider’s office. On the first visit, your provider will:

  • Wipe your inner arm with an antiseptic solution
  • Use a tiny needle to inject a small amount of PPD under the first layer of skin. PPD is a protein that comes from the tuberculosis bacteria. It is not live bacteria, and it will not make you sick.
  • A small bump will form on your forearm. It should go away in a few hours.

Be sure to leave the site uncovered and undisturbed.

After 48-72 hours, you will return to your provider’s office. During this visit, your provider will check the injection site for a reaction that may indicate a TB infection. This includes swelling, redness, and an increase in size.

For a TB test in blood (also called an IGRA test), a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don’t any special preparations for TB skin test or a TB blood test.

Are there any risks to the test?

There is very little risk to having a TB skin test or blood test. For a TB skin test, you may feel a pinch when you get the injection.

For a blood test, you may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If your TB skin test or blood test shows a possible TB infection, your health care provider will probably order more tests to help make a diagnosis. You may also need further testing if your results were negative, but you have symptoms of TB and/or have certain risk factors for TB. Tests that diagnose TB include chest x-rays and tests on a sputum sample. Sputum is a thick mucous coughed up from the lungs. It is different than spit or saliva.

If not treated, TB can be deadly. But most cases of TB can be cured if you take antibiotics as directed by your health care provider. Both active and latent TB should be treated, because latent TB can turn into active TB and become dangerous.

If you have questions about your results, talk to your health care provider.

Is there anything else I need to know about a TB screening?

Treating TB takes much longer than treating other types of bacterial infections. After a few weeks on antibiotics, you will no longer be contagious, but you will still have TB. To cure TB, you need to take antibiotics for at least six to nine months. The length of time depends on your overall health, age, and other factors. It’s important to take the antibiotics for as long as your provider tells you, even if you feel better. Stopping early can cause the infection to come back.

How Tuberculosis Is Diagnosed: Screenings and Tests

Because tuberculosis symptoms can be similar to those of other conditions, it may take time to confirm the correct diagnosis.

Doctors use chest X-rays and blood tests, among other tools, to screen for and help diagnose tuberculosis. Getty Images (2)

The likelihood that an average person in the United States will be exposed to tuberculosis (TB) is low, but if you think you’ve been exposed to the bacteria that causes this infection, it’s important to get tested. People can carry latent TB for years before it becomes active, making them sick. Active tuberculosis poses a public health risk because it can spread to others if left untreated. (1)

“Anybody can get TB. It’s an infectious disease,” says Lee Reichman, MD, MPH, a professor of medicine and epidemiology and the executive director emeritus at Rutgers Global Tuberculosis Institute in Newark, New Jersey. But the disease is pretty hard to spread. It takes six months of eight-hours-per-day contact to get infected with TB or two months of 24-hour contact, he explains.

About 30 percent of people who are exposed to Mycobacterium tuberculosis will develop latent TB, and if that’s left untreated, around 5 to 10 percent of those people could end up getting active tuberculosis disease at some point in their lifetime. (2)

Since tuberculosis bacteria grow slowly and symptoms can be confused with those of other conditions, careful testing is required. Several laboratory and imaging tests may need to be done to definitively diagnose active TB.

Slowing the spread of TB requires catching it early and treating it early. If caught in the latent stage, TB can be treated before the disease becomes active and infectious.

In the United States, screening for latent TB is done in the following populations: (1,3,4)

  • People who have recently come to the United States from a country with a high rate of tuberculosis (including Russia and countries in Latin America, the Caribbean, Africa, and Eastern Europe)
  • People whose work or living arrangements put them in contact with people who have active tuberculosis
  • People who are starting to take a drug that suppresses the immune system, which may reactivate latent tuberculosis
  • People with other diseases that increase the risk of developing active TB once infected, such as insulin-requiring diabetes, end-stage renal disease, prior gastrectomy, or HIV infection
  • People who are taking drugs that block tumor necrosis factor alpha, such as Remicade (infliximab), Humira (adalimumab), or Enbrel (etanercept)

If you’re in a high-risk group, it’s worth having a conversation with your doctor to decide if the testing is right for you, says Hayan Yacoub, MD, an internal medicine practitioner at Austin Regional Clinic in Texas.

The Centers for Disease Control and Prevention (CDC) recommends screening anyone with the following symptoms for active TB: (4)

  • Coughing that lasts for three weeks or longer
  • Weight loss that can’t be explained
  • Coughing up blood
  • Chest pain
  • Loss of appetite
  • Night sweats
  • Fever
  • Fatigue

Before ordering tests, your doctor will check your lymph nodes for swelling, listen to your lungs, discuss your symptoms, and ask a few questions to get a sense of your possible TB exposure. (5)

Screening Tests for Tuberculosis and Who Should Get Them

Screening tests are more often used to find latent TB in people with a weakened immune system or those who may have recently been exposed to someone with active TB. (3,4)

Three tests are used to screen for tuberculosis:

  • A chest X-ray (best used to screen for active TB)
  • A tuberculin skin test
  • Blood tests (interferon gamma release assay, QuantiFERON-TB Gold, and T-Spot)

A chest X-ray is taken to look for changes in the lungs that could show signs of active TB or scars from a previous TB infection. Doctors will look for lesions or anything else that doesn’t appear normal, which could mean a person has pulmonary TB. Spots on your lungs could also mean the immune system is trying to contain the spread of TB bacteria.

A tuberculin skin test, also known as a Mantoux test or PPD (purified protein derivative), is done by injecting a solution containing a protein made from tuberculosis bacteria just under the top layer of skin on the forearm. It’s done in two parts; first, an injection is given, and then the person will return to the doctor’s office in 48 or 72 hours to have the injection site examined. If the skin at the injection site develops a raised red bump, it indicates that the person may be infected with TB. (4,5,6)

If a skin test is positive, doctors will consider a person’s risk factors and then order additional testing to figure out the best course of treatment. The skin test can give a false-positive result if a person has had a prior vaccination with the bacille Calmette-Guérin (BCG) vaccine or is infected with other bacteria that are close relatives of tuberculosis. For this reason, doctors don’t rely on the skin test alone to confirm a diagnosis. (5)

It’s also possible for the skin test to give a false negative. This can happen in people who have been infected very recently or who have HIV/AIDS, or in children and elderly adults.

The brand-name blood tests are approved in the United States for the diagnosis of latent TB infection. A blood test may be ordered on its own or after a positive skin test. Like the tuberculin skin test, the different blood tests offer ways to measure the body’s immune response to the presence of Mycobacterium tuberculosis. The tests are done in a lab after a blood sample is drawn.

The blood tests do not react to the BCG vaccine, so they can help rule out a false positive from a skin test in those who may have had the vaccine.

Diagnostic Tests to Determine Active TB Disease vs. Latent TB Infection

Neither the tuberculin skin test nor any of the blood tests can tell the difference between active and latent disease. Chest X-rays also have their limitations because the effects of TB on the lungs are similar to those of many other conditions.

For a more conclusive diagnosis, other tests are necessary: (6,7,8,9)

  • Sputum is the mucus that comes up when you cough. If a skin or blood test is positive, doctors will take samples of sputum and look for the presence of Mycobacterium tuberculosis. Sputum can also be tested for drug-resistant strains; the results help doctors choose the right medications for treatment. Lab results take about four to eight weeks.
  • Molecular tests can be used to detect the bacteria’s genetic material, which helps identify drug-resistant strains.
  • Samples of sputum or other bodily fluids, as well as tissue samples obtained by a biopsy of the lungs, lymph nodes, or other tissues, may be cultured to grow the bacteria and make it easier to see under a microscope. Culturing TB bacteria can take four to eight weeks before any growth appears, making this a slow process for detecting TB.

A variety of lab tests can also be done to see which drugs will best treat the strain of tuberculosis a person has.

Imaging tests may be used to assist in providing a diagnosis of active tuberculosis: (4,5,6,7,10)

  • X-rays may be done to look for pulmonary TB in the lungs as well as tuberculosis affecting the bones or spine.
  • Computed tomography (CT scans) may be used to look for spinal TB or to get a better view of the lungs if X-ray findings are nonspecific. CT scans offer more detail than X-rays.
  • MRIs of the spine or brain may be done if tuberculosis infection of either is suspected.
  • Bone scans can be used to tell the difference between metastatic (cancerous) lesions and those caused by TB.

Why Testing for HIV Is Recommended When TB Is Diagnosed

Because tuberculosis is closely associated with HIV, it’s become common practice to test for HIV in someone with suspected tuberculosis whose HIV status is not known. This allows treatment for HIV to be started as well, if appropriate, and coordinated with TB treatment. (11)

The CDC recommends HIV testing for anyone who may have TB or who is diagnosed with latent TB. That’s because HIV is a known risk factor for getting infected with latent TB and having it become active. TB is also more deadly for people with HIV. When HIV is identified and treated, outcomes for TB treatment improve. (11)

“Once the HIV is under control, risk of TB recurrence is decreased,” says Alexea Gaffney-Adams, MD, an internist and pediatrician with subspecialty training in infectious disease at Stony Brook Medicine in Smithtown, New York.

Starting Treatment for Tuberculosis After Diagnosis

It can take some time to positively diagnose active tuberculosis. In cases where tuberculosis is strongly suspected, doctors often start treatment before the diagnosis is confirmed by laboratory isolation of the TB bacteria.

Tuberculosis is treated by taking a series of drugs over several months to kill the bacteria. Active TB takes longer to treat than latent TB because the bacteria have multiplied. (6)

Additional reporting by Ingrid Strauch.

Diagnosis


Tuberculosis (TB)

Testing for latent TB

In some circumstances, you may need to have a test to check for latent TB – where you’ve been infected with TB bacteria, but do not have any symptoms.

For example, you may need to have a test if you’ve been in close contact with someone known to have active TB disease involving the lungs, or if you’ve recently spent time in a country where TB levels are high.

If you’ve just moved to the UK from a country where TB is common, you should be given information and advice about the need for testing. Your GP may suggest having a test when you register as a patient.

Mantoux test

The Mantoux test is a widely used test for latent TB. It involves injecting a small amount of a substance called PPD tuberculin into the skin of your forearm. It’s also called the tuberculin skin test (TST).

If you have a latent TB infection, your skin will be sensitive to PPD tuberculin and a small, hard red bump will develop at the site of the injection, usually within 48 to 72 hours of having the test.

If you have a very strong skin reaction, you may need a chest X-ray to confirm whether you have active TB disease.

If you do not have a latent infection, your skin will not react to the Mantoux test. However, as TB can take a long time to develop, you may need to be screened again at a later stage.

If you’ve had the BCG vaccination, you may have a mild skin reaction to the Mantoux test. This does not necessarily mean you have latent TB.

Interferon gamma release assay (IGRA)

The interferon gamma release assay (IGRA) is a blood test for TB that’s becoming more widely available.

The IGRA may be used to help diagnose latent TB:

  • if you have a positive Mantoux test
  • if you previously had the BCG vaccination – the Mantoux test may not be reliable in these cases
  • as part of your TB screening if you’ve just moved to the UK from a country where TB is common
  • as part of a health check when you register with a GP
  • if you’re about to have treatment that will suppress your immune system
  • if you’re a healthcare worker

What to expect with the tuberculosis skin test

A doctor will need to consider several things when interpreting the results of a TB test. The main consideration is the size of the bump on the arm:

  • test bump smaller than 5 millimeters (mm), test result negative
  • test bump larger than 5 mm, test result in the positive range

If the results are in the positive range, the doctor will investigate further by finding out about other factors in a person’s life.

Factors that can affect the results of a TB skin test include:

  • having recent contact with another person with TB
  • working at a medical facility, such as a hospital, care center, or medical lab
  • having TB in the past
  • receiving an organ transplant
  • taking immunosuppressant drugs
  • being HIV positive
  • coming recently from a country where TB is common
  • using injected drugs

Very young children or children exposed to adults with TB are also at a higher risk for TB.

In some cases, the body has a dramatic response to the skin test. This may cause the wheal to grow to over 15 mm in diameter. This indicates a positive outcome no matter what other circumstances there may be.

The outcomes for TB skin tests are not always clear-cut, as explained here:

Share on PinterestThe TB skin test can have a number of factors that may affect the results.

  • Testing positive: This indicates that the body has been infected with the TB bacteria. An infection makes an individual extra sensitive to the tuberculin injection, which causes the test site to grow in diameter.
  • Testing negative: This means the body is unlikely to be infected with the bacteria. It is not sensitive to the tuberculin, and any symptoms are likely to be from something else.
  • False positive: There is the chance for results to show a false positive. People who have been vaccinated against TB, using the bacillus Calmette-Guérin (BCG) vaccine, can sometimes show a positive result, even if they are not infected with the bacteria. This is less common for vaccines given in the United States. It is also possible for the test to read positive falsely if it is not administered correctly, or if the person is infected with bacteria similar to TB.
  • False negative: This can happen when a person is infected with the bacteria. Examples of this are when someone has a weak immune system or has been exposed to pathogens, such as measles and smallpox. People with recent TB infections and very old TB infections can also show false negative test results. If the test is done incorrectly, a false negative might occur.

In many cases, doctors will use additional methods to be sure the results are as accurate as possible.

Fact Sheets

(PDFCdc-pdf– 35k)

Diagnosis of Tuberculosis Disease

When Should You Suspect Tuberculosis (TB)?

TB is a disease caused by Mycobacterium tuberculosis. TB disease should be suspected in persons who have the following symptoms:

  • Unexplained weight loss
  • Loss of appetite
  • Night sweats
  • Fever
  • Fatigue

If TB disease is in the lungs (pulmonary), symptoms may include:

  • Coughing for longer than 3 weeks
  • Hemoptysis (coughing up blood)
  • Chest pain

If TB disease is in other parts of the body (extrapulmonary), symptoms will depend on the area affected.

How Do You Evaluate Persons Suspected of Having TB Disease?

A complete medical evaluation for TB includes the following:

1. Medical History

Clinicians should ask about the patient’s history of TB exposure, infection, or disease. It is also important to consider demographic factors (e.g., country of origin, age, ethnic or racial group, occupation) that may increase the patient’s risk for exposure to TB or to drug-resistant TB. Also, clinicians should determine whether the patient has medical conditions, especially HIV infection, that increase the risk of latent TB infection progressing to TB disease.

2. Physical Examination

A physical exam can provide valuable information about the patient’s overall condition and other factors that may affect how TB is treated, such as HIV infection or other illnesses.

3. Test for TB Infection

The Mantoux tuberculin skin test (TST) or the TB blood test can be used to test for M. tuberculosis infection. Additional tests are required to confirm TB disease. The Mantoux tuberculin skin test is performed by injecting a small amount of fluid called tuberculin into the skin in the lower part of the arm. The test is read within 48 to 72 hours by a trained health care worker, who looks for a reaction (induration) on the arm.

The TB blood test measures the patient’s immune system reaction to M. tuberculosis.

4. Chest Radiograph

A posterior-anterior chest radiograph is used to detect chest abnormalities. Lesions may appear anywhere in the lungs and may differ in size, shape, density, and cavitation. These abnormalities may suggest TB, but cannot be used to definitively diagnose TB. However, a chest radiograph may be used to rule out the possibility of pulmonary TB in a person who has had a positive reaction to a TST or TB blood test and no symptoms of disease.

5. Diagnostic Microbiology

The presence of acid-fast-bacilli (AFB) on a sputum smear or other specimen often indicates TB disease. Acid-fast microscopy is easy and quick, but it does not confirm a diagnosis of TB because some acid-fast-bacilli are not M. tuberculosis. Therefore, a culture is done on all initial samples to confirm the diagnosis. (However, a positive culture is not always necessary to begin or continue treatment for TB.) A positive culture for M. tuberculosis confirms the diagnosis of TB disease. Culture examinations should be completed on all specimens, regardless of AFB smear results. Laboratories should report positive results on smears and cultures within 24 hours by telephone or fax to the primary health care provider and to the state or local TB control program, as required by law.

6. Drug Resistance

For all patients, the initial M. tuberculosis isolate should be tested for drug resistance. It is crucial to identify drug resistance as early as possible to ensure effective treatment. Drug susceptibility patterns should be repeated for patients who do not respond adequately to treatment or who have positive culture results despite 3 months of therapy. Susceptibility results from laboratories should be promptly reported to the primary health care provider and the state or local TB control program.

Additional Information

TB Skin Test

Sources Used in Current Review

Lewinsohn, D. et. al. (2017 January 3). Official American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention Clinical Practice Guidelines: Diagnosis of Tuberculosis in Adults and Children. Clinical Infectious Diseases, Volume 64, Issue 2, 15 January 2017, Pages 111–115. Available online at https://academic.oup.com/cid/article/64/2/111/2811357. Accessed on 5/05/18.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA .

Centers for Disease Control and Prevention (CDC) (2002 August 13, Reviewed). Frequently Asked Questions, Questions and Answers about TB. National Center for HIV, STD and TB Prevention Division of Tuberculosis Elimination . Available online at http://www.cdc.gov/nchstp/tb/faqs/qa.htm.

Mazurek, G. & Villarino, M. (2002 December 18 Updated). Guidelines for Using the QuantiFERON®-TB Test for Diagnosing Latent Mycobacterium tuberculosis Infection. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report . Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/di51cha1.htm.

Tuberculin Purified Protein Derivative (Mantoux) Tubersol. Aventis Pasteur Inc. (Swiftwater, PA) .

QuantiFERON – TB Gold In-Tube: FAQs. Available online at http://www.cellestis.com/. Accessed November 2008.

Guidelines Released for Investigation of Potential Contact with Infectious Tuberculosis

Diagnosis and Treatment of Contacts

On average, 10 contacts are listed for each person with infectious tuberculosis in the United States. Approximately 20 to 30 percent of all contacts have latent tuberculosis infection, and 1 percent have tuberculosis disease. Of those contacts who ultimately will have tuberculosis disease, approximately one half acquire the disease in the first year after exposure. For this reason, contact investigations constitute a crucial prevention strategy.

Efficiently identifying tuberculosis disease and latent tuberculosis infection requires identifying, locating, and evaluating high- and medium-priority contacts who are most at risk. Because they have legally mandated responsibilities for disease control, health departments should establish systems for comprehensive tuberculosis contact investigations. In certain jurisdictions, legal measures are in place to ensure that evaluation and follow-up of contacts occur. The use of existing communicable disease laws that protect the health of the community (if applicable to contacts) should be considered for contacts who decline examinations, with the least restrictive measures applied first.

In 2002, for the first time, the percentage of patients with tuberculosis who were born outside the United States was greater than 50 percent; this proportion continues to increase. Because immigrants are likely to settle in communities in which persons of similar origin reside, multiple contacts of foreign-born index patients also are foreign born. Contacts who come from countries where both bacille Calmette-Guèrin (BCG) vaccination and tuberculosis are common are more likely than other immigrants to have positive skin test results when they arrive in the United States. They also are more likely to demonstrate the booster phenomenon on a postexposure test. Although valuable in preventing severe forms of disease in young children in countries where tuberculosis is endemic, BCG vaccination provides imperfect protection and causes tuberculin sensitivity in certain recipients for a variable period. Tuberculin skin tests cannot distinguish reactions related to remote infection or BCG vaccination from those caused by recent infection with M. tuberculosis; boosting related to BCG or remote infection compounds the interpretation of positive results.

A positive tuberculin skin test result in a foreign-born or BCG-vaccinated person should be interpreted as evidence of recent M. tuberculosis infection in contacts of persons with infectious disease. These contacts should be evaluated for tuberculosis disease and offered a course of treatment for latent tuberculosis infection.

TUBERCULIN SKIN TESTING

All contacts classified as having high or medium priority who do not have a documented previous positive tuberculin skin test result or previous tuberculosis disease should receive a skin test at the initial encounter. If that is not possible, then the test should be administered within seven working days of listing high-priority contacts and within 14 days of listing medium-priority contacts. For interpreting the skin test reaction, an induration transverse diameter of at least 5 mm is positive for any contact.

Serial tuberculin testing programs routinely administer a two-step test at entry into the program. This detects boosting of sensitivity and can avoid misclassifying future positive results as new infections. The two-step procedure typically should not be used for testing contacts; a contact whose second test result is positive after an initial negative result should be classified as recently infected.

Postexposure Tuberculin Skin Testing

Among persons who have been sensitized by M. tuberculosis infection, the intradermal tuberculin from the skin test can result in a delayed-type (cellular) hypersensitivity reaction. Depending on the source of recommendations, the estimated interval between infection and detectable skin test reactivity (referred to as the window period) is two to 12 weeks. However, reinterpretation of data collected previously indicates that eight weeks is the limit of this window period. Consequently, the National Tuberculosis Controllers Association and the CDC recommend that the window period be decreased to eight to 10 weeks after exposure ends. A negative test result obtained less than eight weeks after exposure is considered unreliable for excluding infection, and a follow-up test at the end of the window period is therefore recommended.

Low-priority contacts have had limited exposure to the index patient and a low probability of recent infection; a positive result from a second skin test among these contacts would more likely represent boosting of sensitivity. A single skin test, probably at the end of the window period, is preferred. However, diagnostic evaluation of any contact who has tuberculosis symptoms should be immediate, regardless of skin test results.

Nonspecific or remote delayed-type hypersensitivity response to tuberculin (purified protein derivative in the skin test) occasionally wanes or disappears over time. Subsequent tuberculin skin tests can restore responsiveness; this is called boosting or the booster phenomenon. For contacts who receive two skin tests, the booster phenomenon can be misinterpreted as evidence of recent infection. This misinterpretation is more likely to occur for foreign-born contacts than it is for those born in the United States.

Skin test conversion refers to a change from a negative to a positive result. To increase the relative certainty that the person has been infected with M. tuberculosis in the interval between tests, the standard U.S. definition for conversion includes a maximum time (two years) between skin tests and a minimum increase (10 mm) in reaction size. With the 5-mm cutoff size used for interpreting any single skin test result obtained in contact investigations, the standard definition for conversion typically is irrelevant. For these guidelines, contacts who have a positive result after a previous negative result are said to have had a change in tuberculin status from negative to positive.

MEDICAL EVALUATION

All contacts whose skin test reaction induration diameter is at least 5 mm or who report any symptoms consistent with tuberculosis disease should undergo further examination and diagnostic testing for tuberculosis, typically starting with chest radiography. Collection of specimens for mycobacteriologic testing (e.g., sputum) is decided on a case-by-case basis and is not recommended for healthy contacts with normal chest radiography results. All contacts who are assigned a high priority because of special susceptibility or vulnerability to tuberculosis disease should undergo further examination and diagnostic testing regardless of whether they have a positive skin test result or are ill.

EVALUATION AND FOLLOW-UP OF SPECIFIC GROUPS OF CONTACTS

Because children younger than five years are more susceptible to tuberculosis disease and more vulnerable to invasive, fatal forms of tuberculosis disease, they are assigned a high priority as contacts and should receive a full diagnostic medical evaluation, including chest radiography. If an initial skin test induration diameter is less than 5 mm and the interval since last exposure is less than eight weeks, treatment for presumptive M. tuberculosis infection (i.e., window prophylaxis) is recommended after tuberculosis disease has been excluded by medical examination. After a second skin test administered eight to 10 weeks postexposure, the decision to treat is reconsidered. If the second test result is negative, treatment should be discontinued and the child, if healthy, should be discharged from medical supervision. If the second result is positive, the full course of treatment for latent M. tuberculosis infection should be completed.

Contacts with immunocompromising conditions should receive similar care. In addition, even if a tuberculin skin test administered at least eight weeks after the end of exposure yields a negative result, a full course of treatment for latent M. tuberculosis infection is recommended after a medical evaluation to exclude tuberculosis disease. The decision to administer complete treatment can be modified by other evidence concerning the estimated extent of transmission.

Most other high- or medium-priority contacts who are immunocompetent adults or children five years or older can be tested and evaluated as described in Figure 2. Treatment is recommended for contacts who receive a diagnosis of latent M. tuberculosis infection.

Evaluation and Treatment for Infectious Tuberculosis

Figure 2.

Algorithm for evaluation and treatment of immunocompetent adults and children five years and older who have had contact with a person infected with tuberculosis. (TST = tuberculin skin test; TB = tuberculosis.)

Figure 2.

Algorithm for evaluation and treatment of immunocompetent adults and children five years and older who have had contact with a person infected with tuberculosis. (TST = tuberculin skin test; TB = tuberculosis.)

Evaluation of low-priority contacts is more flexible. The skin test may be delayed until after the window period, thereby negating the need for a second test. Treatment also is recommended for these contacts if they are diagnosed with latent M. tuberculosis infection.

TREATMENT FOR CONTACTS WITH LATENT TUBERCULOSIS INFECTION

One of the national health objectives for 2010 is to complete treatment in 85 percent of contacts who have latent tuberculosis infection. However, reported rates of treatment initiation and completion have fallen short of national objectives. To increase these rates, health department tuberculosis control programs must invest in systems for increasing the numbers of infected contacts who are completely treated. These include: (1) focusing resources on the contacts most in need of treatment; (2) monitoring treatment, including that of contacts who receive care outside the health department; and (3) providing directly observed therapy, incentives, and enablers.

Contacts identified as having a positive tuberculin skin test result are regarded as recently infected with M. tuberculosis, which puts them at heightened risk for tuberculosis disease. Moreover, contacts with greater durations or intensities of exposure are more likely to be infected and to have tuberculosis disease if infected. A focus first on high-priority and next on medium-priority contacts is recommended in allocating resources for starting and completing treatment of contacts.

Decisions to treat contacts who have documentation of a previous positive skin test result or tuberculosis disease for presumed latent tuberculosis infection must be individualized because their risk for tuberculosis disease is unknown. Considerations for the decision include previous treatment for latent tuberculosis infection, medical conditions putting the contact at risk for tuberculosis disease, and the duration and intensity of exposure. Treatment of presumed latent tuberculosis infection is recommended for all contacts with HIV infection in this situation (after tuberculosis disease has been excluded), whether they received treatment previously.

WINDOW-PERIOD PROPHYLAXIS

Treatment during the window period has been recommended for susceptible and vulnerable contacts to prevent rapidly emerging tuberculosis disease. The evidence for this practice is inferential, but all models and theories support it. Groups of contacts who are likely to benefit from a full treatment course (beyond just window-period treatment) include those with HIV infection, those taking immunosuppressive therapy for organ transplantation, and persons taking tumor necrosis factor-α antagonists. The risks for tuberculosis are less clear for patients who chronically take the equivalent of more than 15 mg per day of prednisone. Once tuberculosis disease has been ruled out, prophylactic treatment of presumed M. tuberculosis infection is recommended as an option for all these groups. The decision of whether to treat individual contacts who have negative skin test results should take into consideration two factors:

  • The frequency, duration, and intensity of exposure (even brief exposure in a confined space to a highly contagious patient with tuberculosis probably warrants the same concern as extended exposure to less contagious patients); and

  • Corroborative evidence of transmission from the index patient (a substantial fraction of contacts having positive skin test results implies contagiousness).

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